1. Field of the Invention
This invention relates to a semiconductor laser module wherein a semiconductor laser chip and an optical fiber are combined, and a method of positioning the components of such a semiconductor laser module.
2. Description of the Background Art
A single mode optical fiber having a core, the diameter thereof being relatively small (for example, 10 .mu.m), is now widely used as an optical transmission path, since the transmission loss thereof is relatively low and it can be applied to a wide frequency range.
To obtain a long distance transmission by such an optical fiber, an optical beam emitted from a semiconductor laser at an emission angle must be connected to a small incident face of the optical fiber with a high coupling efficiency.
If the laser beam is reflected at the connecting portions of the optical fiber or in optical devices in the optical paths, and if the reflected beam is returned to the semiconductor laser, the oscillation of the laser beam emission becomes unstable and, as a result, noise in the laser beam signal may be increased. Therefore, a semiconductor laser module having an isolation function is required.
Also, the components, such as the semiconductor laser, collimator lens, focussing lens, and the like, including in the semiconductor laser module, must be precisely positioned relative to each other, so that a laser beam emitted from the semiconductor laser is introduced to the optical fiber with a high coupling efficiency.
In the prior art, a known semiconductor laser module comprises: a semiconductor laser chip for emitting a laser beam, a collimator lens for collimating the laser beam to a collimated beam, a focussing lens for focussing the collimated beam, and an optical fiber having an inclined input face to which the laser beam from the focussing lens is input. Such an inclined input face of the optical fiber is advantageous for preventing a return of the laser beam reflected at the input face to the semiconductor laser.